In known fuel filler assemblies fitted to currently marketed vehicles, the fuel filler and cap are housed inside a compartment which is recessed in the vehicle body and closed by a lid kept in the closed position by a spring or a snap-on device; and the cap is normally separable from the filler body pipe, or tube, and is normally screwed manually onto the filler tube or pipe and/or locked by means of a key-operated locking device.
When refueling, the cap is removed from the filler body or tube and set aside on any convenient supporting surface; and, at times, once the vehicle is refueled, the lid may inadvertently be closed with the cap fitted improperly to the filler tube or pipe, or even with no cap at all, thus resulting in extremely dangerous diffusion of fuel vapors and fuel leakage.